Radio Design Labs HR-ADC1

[danjp]

I am currently looking for a replacement interface comparable with my old Lynx L22 card which still works well but is not Linux compatible.
I have purchased a SMSL D6s (based on the review here) as a replacement for the DAC portion which works great and now I am looking for the ADC portion.

I need a fully compliant class 2 USB interface that works well in Linux as that will be my main computer for this.
So what I would like to get is a USB ADC with sample rates up to 192Khz/24bit with a frequency response flat out to at least 80KHz and a flat noise floor like the L22 has.
I will be using this to digitize various audio sources consisting of both balanced and unbalanced interfaces and for various measurement purposes. I am an engineer and also use the L22 for testing my custom designs hence the need for an extended frequency response and flat noise floor.

I did try the Topping E2x2 but I had way too many issues with noise spikes and EMI interference when using the line inputs in unbalanced mode even when using heavily shielded cables. I had noise spikes that started at 8KHz and repeated every 8Khz over a very large range. I could not figure out where this was coming from. I could also see a lot of EMI interference that was showing up as low frequency noise. I was probably getting this from the cell tower that I live close to.
My best guess is that the analog input was optimized for balanced operation and is relying on the input's differential opamp CMRR to minimize noise and that there are no EMI filters in the input path to prevent both common mode and differential interference. Unbalanced mode just seems to tie the minus input to ground and without an EMI filter on the input the CMRR does very little to deal with differential noise.
I did try using both USB power and external power and seen the same in both although it was slightly better with the external supply but not by much.
No matter what I tried, I could not get them to go away. They were as high as -85dB re full scale and changed amplitude with the gain setting.

If I used the balanced inputs, then it was pretty quiet but I also need the interface to work well in unbalanced mode also.
I should also state that my Lynx L22 does not show any of these issues in either balanced or unbalanced mode using the same computer.
This coupled with the my inability to get the software to install in Windows finally caused me to send the unit back.

So now the one unit I am now looking at is the Radio Design Labs HR-ADC1.

https://rdlnet.com/product/hr-adc1/

It has discrete balanced and unbalanced inputs so hopefully these are both optimized for the application.
Unfortunately, I am not able to find any measurements at all on the web for this unit and the few reviews I found people said the unit worked well.
But at almost $900 I would really like to see some measurements to justify the cost. There are only generic specs on their web site.

So I would like to ask if anyone on this site has used the HR-ADC1 and if so, do you have any information to share I would really appreciate it.

Thanks, Dan

 

[DVDdoug]

I did try using both USB power and external power and...

USB power tends to be noisy and sometimes that noise gets into the analog electronics, especially the high-gain mic preamps which amplifies any noise. Usually it's high-frequency "whine". And then you don't know if you should blame the computer for having noisy power or the interface for having insufficient filtering. That might have been the source of the 8kHz noise.

An interface with it's own separate power supply should eliminate that possibility.

 

[AnalogSteph]

How many different unbalanced sources do you have? Adapting those for use with a balanced input fundamentally is quite easy (match impedances by adding some to the ground leg that's mimicking the signal leg, then make sure common-mode voltage difference between both devices is kept within reasonable levels). Being stuck with unbalanced outputs and a balanced input is a much better position than the other way round.

The application kind of screams "Cosmos ADC(iso) + Scaler" to me.

 

[danjp]

Yes I was looking at the "Cosmos ADC(iso) + Scaler" as a possible replacement but I settled on the RDL HR-ADC1 as it does everything I need and I was able to find one for an excellent price. My initial measurements are good with no spurs like with the E2x2. The only thing that does not compare to the Lynx L22 is that the A/D used has noise shaping that starts to increase around 60KHz or so. Not terrible (10dB rise at 96KHz), but unlike the Lynx L22 with the AKM AK5394 ADC which has a flat noise floor out to 100KHz.
In addition, the RDL unit begins to roll off around 65KHz while the Lynx L22 stays flat to around 80KHz. But I was able to get the RDL working reliably using optical SPDIF with a simple Toslink to USB interface so Linux is able to use it with the generic USB driver unlike the Lynx which needs to use the OSSV4 sound system to provide a driver. So overall the RDL is a fairly good replacement for the Lynx L22 but is still not quite as good but both sound very close to each other with a slight edge going to the Lynx card. I only wish Lynx would support Linux as I think they definately have the best A/Ds available.